Investigation of the performance of short diffusers configurations for different inflow profiles

Diffusers are used to connect the outlet of axial fans to the following piping. In thermal power plants the diffuser design is often restricted by limited installation space. Two different diffuser configurations for limited diffuser length and fixed inlet and outlet diameter are studied at a scaled diffuser test rig. Configuration 1 combines an annular diffuser and a Carnot diffuser to achieve the required diffuser outlet diameter. Configuration 2 consists of an annular diffuser (diffuser 1) and a diffuser 2 with installed guiding bodies. These bodies are arranged in a star-like configuration and reduce the effective opening angle of the diffuser. The tests have been carried out with different inlet velocity profiles. Configuration 1 was more sensitive on inlet profile variation regarding flow separation. The pressure recovery for both configurations is compared for different positions downstream the diffuser. There is a significant static pressure increase due to a reduction of over-speed areas.